How does the Silky cup stay in place?

How does the Silky cup stay in place?

 

The Silky Cup (reusable menstrual cup) is bell shaped, fitting snugly against the uterine walls – not up near the cervix and inside the vaginal opening. The rim and the tiny holes near the top allow the cup is form suction to stay in place securely. It stays in place and collects menstrual bleeding that way.